Selective signaling system



M ay 9, 1933. c. SQ'DEMAREST SELECTIVE SIGNALING, SYSTEM 4 sheets-sheet 1 Filed Aug. 18 1932 INVENTOR 6', (filklmaicesi BY ATTORNEY May 9 1933. c. s. DEMAREST SELECTIVE SIGNALING SYSTEM Filed Aug. 18 1932 4 Sheets-Sheet 2 INVENTOR Y; 6'; JIDeW/ BY ATTORNEY May 9, 1931?. c. s. DEMARE'ST SELECTIVE S IGNALING SYSTEM .Filed Aug. 18 i932 Zine 7002 ATTORN EY May 9, 1933. c. s. DEMAREST SELECTIVE SIGNALING SYSTEM Fil ed Aug. 18 1932 4 Sheets-Sheet 4 I INVENTOE 6. lififllmwnas/t ATTORNEY Patented May 9, 1933 UNITED STATES PATENT orrlce- CHARLES S. DEMABEST, OI BIDGEWOOD, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- I PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK SELECTIVE SIGNALING SYSTEM Application filed August 18, 1932. Serial No. 629,382.

The invention relates to electrical circuits resistance from anode to cathode changes and more particularly to improved means froma very high value,. substantially that of signaling over telephone or telegraph of the insulation, to a negligible value when channels, in which a predetermined code an arc is established by variation of the inconsisting of current impulses selects and put voltage. 4 55 signals one out of a plurality of signal re- This invention may be utilized in a variceiving devices connected to the telephone ety of arrangements for selective signaling or telegraph channel. 1 Switching. Other objects, uses and fea- Heretofore, selective signaling devices tures of the invention will appear more fully have utilized some form of electro-mechanifrom the detailed description thereof herein 60 cally operated selector which in response to after given. the signaling impulses completes local cir- The invention may be more fully undercuits and operates the desired signal. Such stood from the following description todevices may also serve to switch the telegethenwith the accompanying drawings in phone or telegraph channel, as. in the selecthe Figures 1, 2, 3, 4' and 5 of which the 65 tors used in the various forms of automatic, invention is illustrated. Similar reference dial operated, telephone systems. As the characters have been used to denote like electro-mechanical type of selector requires parts in all'of the figures. direct current for its operation and also re- In the arrangement shown in Figs. .1, 2"

quires s'ufiicient current to o erate relativeand 3 the gas filled thermionic tubes-26and 70 ly heavyarmatures, it has Teen necessary 161 may be said to take the place of the either to transmit the signaling impulses as stepping electromagnet of the ordinary sedirect current or to provide suitable detectlector switch in that they serve to connect ing means to convert A. C. impulses to the signaling impulses selectively to the con- D. C. impulses. Owing to the magnitude of necting tubes 109, 117 or 184 and 186, the the selector operating currents, it has also latter serving to connectthe incoming line been necessary to provide relaying or, reover wires and 46 to any of the desired peating apparatus in order to provide sufiilines 1001, or 1002, when operated. Tubes 53 cient current except in the case of very short and are arranged to connect the incomdistances. The ordinary type of selector, ing line on conductors 45' and 46 normally having mechanicalmoving parts requires adline 1000. .Tubes. 93 and 14.9 serve to exjustment and proper attention to operate sattinguish the arc in tubes 53 and 60 or in 109 lsfactorily. It, furthermore, is limited in and 117, respectively, thus releasing the cons d of operation, due to the inertia of nections previously established, while tube t ese moving arts. This invention pro- 224 serves to extinguish the arc in all other vides a device or selective signaling or setubes except 53 and 60 which reignite when lective switching, which will operate on very other tubes are extinguished and the circuit small amounts of energy, either A. C. or restored to its normal condition. D. C., and which has-no mechanical moving Before tracing the operation of the cirparts. These features are of particular adcuit in detail, reference will be made to vantage when the device is to be operated Figs. 4 and 5 which illustrate certain control by impulses sent through a transmission arrangements for gas filled thermionic tubes channel providing a voice-frequency band, used in the complete circuit as shown on as over telephone circuits, either voice fre- Figs. 1, 2 and 3. As these arrangements or quency or carrier, or over'a radiotelephone both of them are used in connection with circuit. D. C. or carrier current telegraph many of the tubes of the other figuresof channels may also be used to advantage in the drawings, it will facilitate explanation 1 connection with this invention. to consider these particular features sep- The inventionntilizes the properties of arately. 53 the gas-filled thermionic tube, wherein the Fig. 4 illustrates an arrangement which outputof rectifier303 will up condenser 307 toLthe reverse polarity, but

may be described as a slow-operate control circuit for a gas filled thermionic tube. It ma also serve as a marginal operation contro In Fig. 4, conductors 300 and'30l represent the input circuit to the tube 308. Alternating current signals received over conductors 300 and 301 are applied through transformer 302 to the grid circuit which contains rectifier element 303, resistances 304 and 305, condensers 306 and 307, and biasing battery 7. The operation of this grid circuit may be seen from the following considerations. It will be supposed first that no alternating current is applied to the conductors 300 and 301, and that no are exists in the tube 308. Battery 7 maintains the grid at a potential sufficiently negative to prevent the are from bein established between anode and cathode, by virtue of thepotential applied to the anode of tube 308 from battery 310 through resistance 309. Battery 8 sup lies cathode heating power, the cathode 0 tube 308 beingof the indirectly heated type.

If now an alternating current be applied to conductors 300 and 301. and thus to the primary winding of transformer 302, rectification in rectifier element 303 will take place, the polarity of the rectifier being assumed such that current flows in the direction from the terminal indicated by the triangular symbol to .the terminal indicated by the bar symbol, and current will flow from the lower end of the, rectifier 303 through resistance 304 to condenser 307,

which is charged in such a manner that the polarity will reverse, overriding the voltage from biasing battery 7 and causing the arc to be established in the tube. This condenser 307 willnot charge immediately however, the rate of charging being controlled b resistances 304 and 305. It should be observed that prior to the application of an alternating current input to conductors 300' and 301 condenser 307 will be charged to the voltage of battery 7. One pole, the positive, of battery 7 is connected to the cathode ofthe tube and one terminal of condenser 307, while the negative pole of battery 7 is connected to the other terminal-of condenser 307 throughthe secondary winding of transformer 302 and resistance 305 in series. The tend to charge the voltage available for this purpose is determined by the relative magnitudes of resistances 304 and 305, and the amplitude of the alternating current input. Condenser 306 does not ordinarily serve any purpose, except that it permits marginal instantaneous operation for A. C. inputs of such magnitude that the peak A. C. voltage applied to 'the grid of tube 308 through the capacity potentiometer formed by condensers 306 and 307 is sufiicient to cause the grid to swing similar manner to the starting arrangement shown in Fig. 4. If an A. C. input has been applied to conductors 311 and 312, and if the peak value of the voltageacross the secondary of transformer 313 resulting therefrom is suflicient to swing the grid of tube 314 sufiiciently positive to overcome the neg ative bias from battery 7, an arc will strike. The path of the are current will be from the positive pole of battery 315 through resistance 316 to the anode of tube 314, thence through the arc path to the cathode of tube 314 and thence to the negative pole of battery 315. The grid now loses control, and the arc will continue even though the input be removedfrom conductors 311 and 312.

If now-switch 322 be closed alternating current from generator 323' will flow through rectifier elements 317, 318, 319 and 320, and through resistance 316, also charging condenser 321, in such a manner as to produce an E. M. F. across resistance 316 opposing the voltage of battery 315 and reducing the voltage between anode and cathode of tube 314 to zero or to a value such that the anode is negative with respect to the cathode, interrupting the are. If switch 322 remains closed long enough after the E. M. F. has built up by charging condenser 321 to stop the discharge, and for the gas in the tube to become deionized so that the grid regains control, the arc will not then reestablish on opening switch 322 until input voltage is again applied to conductors 311 and *312.

While the arrangement shown works with but slight delay, by utilizing a circuit similar to that in the grid of the tube 308 in Fig. 4, the plate circuit could be made slowrelease, the are becoming extinguished a predetermined time after the closure of switch 322.

With the arrangements thus described in mind, it will be possible to trace in detail the operation of the arrangements of the invention shown on Figs. 1, 2 and 3, with Fig. 2 placed to the right of the right of Fig. 2.

In Fig. 1, generator 1 is a source of alternating current for signaling, pulses of which under control of key or dial 2 are sent over line 3 and 4 to the control circuits. The telephone line 45 and 46 connects subscribers telephone set 43 and ring- Fig. 1 and Fig. 3 to er and induction coil constituting bell box v and 4, but for simplicity separate circuits are here shown.

Tube 6 serves as a relay or repeater of signaling impulses, so that the pulses applied to control tubes 26, 161 and 224 will be of uniform .amplitude. Conductors 3 and 4 are terminated in resistance 5, connected between grid and cathode to tube 6.

Batteries 7 and 8 supply grid bias and cathode heating power. Batteries having the same reference characters and performing similar functions have been shown in connection with other of the gas filled tubes in the drawings. The anode circuit of tube 6 contains potentiometer 10, and the secondar of transformer 9 in series with anode battery 12. The primary oftransformer 9 is connected to generator ll which supplies alternating current of a frequency F which is large compared with the number of pulses per second sent by dial or signaling key 2. The voltage induced in the secondary of transformer 9 is such that on alternate half cycles the anode of tube 6 becomes negative with respect to the cathode thereof, so that anode current will flow in tube 6 during the other alternate half cycles of the voltage across the secondary f transformer 9 provided that the grid of tube 6 is sufficiently positive so that the arc will strike. The voltage applied to grid of tube 6 will be equal tothe voltage dro across resistance due to current theret rough from generator 1 when key 2 is closed, and the biasing voltage of battery 7. The voltage from generator 1 is alternating and of such a magnitude that once every half cycle it will override the negative bias of battery 7.

The resistance of potentiometer 10 limits the current through the arc of tube 6. A pulsating current flows through this device, as a result of the nature of the anode current of tube 6 as previously explained. A portion of the alternating voltage drop in 10, as determined by the position of the moving contact is applied to transformer 17 over conductors 14 and 15. Condenser 16 prevents the flow of directcurrent in this circuit. The secondary of transformer17 connects to the grid of tube 26 through a slow-operate circuit of the type shown in Fig. 4 and previously described. This cir-' cuit is so adjusted that substantially all of one dial pulse of normal length will be required to establish an arc in the anode circuit of tube 26.

As soon as an arc is established in gas filled thermionic tube 26, an A. G. path is completed from the A. C. drop in potentiometer 10 over conductors 14 and 15, through conductor 1400, condenser 1402, conductor 1401 to the cathode of tube 26, thence over conductor 42 to resistance 40 to conductor 41 and thence to transformer 152 shown on Fig. 2. The A. C. path may be traced throu h condenser 153 andthe primary of trans ormer 152 to conductor 19 and thence to condenser 18, on Fig. 1, and therethrough to conductor 15.

As previously stated, the major portion of the first dial pulse will be consumed in charging condenser 27 to the voltage required to cause tube 26 to arc. Alternating current will therefore only flow in the circuit just traced for the brief remaining portion of the first dial pulse, and this will be too short to permit the slow to operate circuit interposed between the secondary of transformer 152 and tube 161 to charge condenser 160. Tube 161 will therefore not operate on the first pulse. It will be noted that alternating current in the path traced above flows through resistance 40. An alternating potential drop will therefore exist between conductors 41 and 42. This potential will cause alternating current to flow from conductor 41 to conductors 410, 411 and 412. From each of these, current will flow through the primaries of transformers 119, 94 and 112, respectively, to conductors 420, 421 and 42 and thence back over conductor 42 to resistance 40.

The voltage thus induced in the secondaries of transformers 119, 94 and 112 will cause arcs to be established in tubes 117,93 and 109, as the positive half cycles of these induced voltages will override the negative bias due to the biasing batteries designated by the symbol 7.

The establishment of arcs in tubes 109 and 117 completes an A. C. path from conductors 49 and 50 to which the incoming line is connected through repeating coil 47 by way of condensers 110 and 111 to conductors 113 and 114 which are connected to the line designated 1001. The establishment of the arc in tube 93 completes an A. C. path from the ungrounded terminal of generator 89, through condenser 90, the primary of transformer 91 to the anode of tube 93, through the arc path of the aforesaid tube to the cathode, thence to ground and to the grounded terminal of generator 89. The alternating voltage induced in the secondary of transformer 91 passes over conductors 87 and 88 to transformers 76 and 86. The secondary of transformer 76 is connected to the rectifier elements 66, 67, 68 and 69, which form a circuit arrangement together wit-h resistance and condenser 70 like that shown in Fig. 5. The secondary of transformer;86 is similarly connected to rectifier elements 78, 79, and 81 which together with resistance 77 and condenser 85 form another device like that shown on Fig. 5. As a result of the passage of alternating current through the primary of transformer 91, and the a plication of an alternating voltage from t e secondary of transformer 91 over conductors 87 and 88 to transformers 76 and 86, an al-' ternating voltage will appear across the secondarles of the last' named transformers and build up voltages in resistances and 77, so stopping the arcs in tubes 53 and 60, and thereby disconnecting the incoming line from line 1000.

Thus the first dial pulse has transferred the connection of the incoming line from line 1000 to line 1001. Tubes 93 and 26 remain in the arcing condition. A second dial pulse will now flow on over the path established through tube 26 when in the arcing condition to tube 161 as described above, and will be of sufiicient duration so that the slow operate circuit between the secondary of transformer 152, which circuit is composed of rectifier I55,'resistances 156, 157, 158, and condensers 159 and 160 arranged like those shown in Fig. 4, will be operated, starting an arc in tube 161. The last ortion of the second dial pulse will, as be ore, be transmitted through a circuit com leted by the arc path of tube 161, and wil cause tubes 174, 184 and 186 to operate. I

The path of the second dial pulse may be traced in detail as follows: The incoming pulse from enerator 1 during the closure of contacts 2 ows over conductor 3, through resistance 5 to conductor 4. Tube 6 operates and remains operated for the duration of the pulse, being quenched at the next negative half cycle of generator 11 after the contacts 2 have opened. Alternating current superimposed on the direct current from battery 12 by the action of generator 11 through transformer 9 will, as before, flow through resistance 10 and the drop in this resistance is applied to transformer 17. Since tube 26 is already in the arcing state due to the first dial pulse,'nothi'ng will result from the alternating current flowing in the secondary of transformer 17. Alternating current will also flow through condenser 18, over conductor 19 to transformer 152, through condenser 153 to conductor 41, through resistance 40 to the anode of tube 26, through the arc paththereof overconductor 1401, through condenser 1402 to conductor 1400 and to conductor 14, and over this back to resistance '10. As stated, the delay circuit between transformer 152 and thegrid of tube 161 will require most of the duration of the second pulse before an arc strikes in tube 161. Upon the striking of the arc in tube 161 a path is completed from conductors 19 through condenser 154, to conductor 190 through the primary .of transformer 217 and condenser 218 toconductor 171, through resistance 163 to and 'through the arc path in tube 161, through condenser 227 to conductor 41 to and through resistance 40 to the arc path of tube 26, to conductor 1401, through condenser 1402 to conductor 1400 to conductor 14. The A. C.

connect conductors 49 and 50 to conductors 201 and 202 of line 1002, through the arc paths of tubes 184 and 186 and condensers 200 and 201, thereby connecting the incoming line to line 1002. At the same time that alternating voltage is impressed between conductors 171 and 172, an alternating voltage will be set up between conductors 1710 and 1720 which are branches of 171 and 172, and connect to the primary of transformer 150. The voltage induced in the secondary of this transformer will cause an arc to be established in tube 149. When this takes place an A. C. circuit is completed from the ungrounded terminal of enerator 145, through condenser 146, the primary of transformer 1430, are path in tube 149, ground, to the grounded terminal of generator 145. The alternating voltage induced in the secondary of transformer 1430 passes over conductors 143 and 144 to the primaries of transformers 132 and 142. The secondaries of these transformers are connected to rectifier circuits in the plate circuits of tubes 109 and 117, which are made up of rectifier elements 124, 125,1126 and 127 or 134, 135, 136 and 137, respectively, and to which are also connected resistance 123 and capacity 128, or resistance 133 and capacity 138, respectively. These circuits are identical with that shown in Fig. 5 and on the application of alternating current to transformers 132 and 142 function to stop the arcs in the tubes 109 and 117, so disconnecting conductors 49 and 50 from conductors 113 and 114 of line 1001.

As the remainder of the second dial pulse after tube 161 passes current is too short to operate the delay circuit interposed between the grid of tube 224 and transformer 217, tube 224 will not pass current at this time. Thus it will be seen that initially the incoming line is connected to line 1000; one dial pulse transfers the connection to line 1001, while two pulses transfer the connection to line 1002. By connecting additional tube circuits between the points a and b, c and d, e and f, g and h, and k, l and m, n and p, g and 1', s and t, it is obvious that other circuit connections for three, four, or other numbers of dial pulses could be made. If, however, pulses equal to a tot-a1, the number of. lines (three in the circuits shown on Fi 1, 2 and.3) be sent in, it is easily seen t at on the next impulse after that operating tube 161, tube 224 will pass 1061 and 1071 are connected to the primaries of transformers 213 and 214, the secondaries of which are connected to circuits similar to that in Fig. 5 in the anode circuits of tubes 184 and 186. These circuits are made up of rectifier elements 191, 192, 193 and 194, a s

o 205, 206, 207 and 208, condensers 105 I and 212, and resistances 189 and 204. As a result, tubes 184 and 186 will be extinguished shortly after the arc is established in tube 224. Conductors 1060 and 1070 connect directly to a rectifier circuit like that of Fig. 5- in the plate circuit of tube 149, which is composed of rectifiers 176, 177, 178 and 179, condenser 180 and resistance 175. Conductors 106 and 107 connect to another similar rectifier circuit in the plate circuit of tube 93 composed of rectifiers 97, 98, 99 and 100,

. extin resistance 96 and condenser 104. The arcs in tubes 93 and 149 will also, therefore, be hed shortly after an arc is started in tu 224. Nothing will result from the interruption of current in tube 149, but in the case of tube 93 this will remove the input to the rectifiers in the plate circuits of tubes 53 and and as the grids of these tubes are biasedpositively the arcs therein will restrike, connecting conductors 49 and '50 to conductors 61 and 62 of line 1000 by way of the arc paths in the aforementioned tubes and condensers 54 and 55.

At the same time alternating current will flow out from the tertiary winding of transformer 225 to a rectifier circuit of the type shown in Fig. 5 in the plate circuit of tube 26. This circuit is composed of rectifiers 30, 3 1, 32 and 33, resistance 29 and condenser 28. The are in tube 26 will thus be extinguished. The primary of'transformer 237 is bridged across conductors 38 and 39 and its secondary connected to a circuit like that of Fig. 5, in plate circuit of tube 161. This circuit is made up of rectifiers 165,

7 166, 167 and 168, resistance 164 and condenser 169. Tube 161 will, therefore, also be extinguished. There is also provided a circuit similar to the grid circuit rectifier unit of Fig. 4, but having larger current capacity, brldged across conductors 38 and 39 and arranged to charge up condenser 228, and build up a drop in resistor 229, which is in series in the plate circuit of tube 224, connected between the tube and plate battery 235. This circuitis so proportioned as to values of resistances 230 and 229 and to that of a rotary selector switch w ich steps around to normal again if one more impulse be sent into it. than the total number of steps on the switch.

\Vhile the arrangements described are particularly adapted to the step-by-step operation of groups of gas filled tubes, the principles herein disclosed are capable of application to many other uses for the selective switching of communication channels. Accordingly, while the invention has been described as embodied in certain specific arrangements, it is understood that it is capable of embodiment in many and other widely varied forms without departin from the spirit of the invention as defined y the appended claims.

-What is claimed is:

1. A signaling system comprising a signal transmitting set, a transmission line connected to said signal transmitting set and extending to a plurality of positions at an ofiice, individual lines at each of said positions, a set of gas filled tubes at each of said ositions, means at each of said positions or connecting the individual line thereat to said transmission line over the cathodeanode circuits of the set of gas filled tubes thereat, and a set of progressively operated gas filled tubes for controlling the operation of the sets of gas filled tubes at each of said positions.

2. A signaling system comprising a signal transmitting set, a transmission line connected to said signal transmitting set and extending to a plurality of positions at an ofiice, individual lines at each of said positions, a set of gas filled tubes at each of said ositions, means at each of said positions or connecting the individual line thereat to said transmission line over the cathodeanode circuits of the set of gas filled tubes thereat, means for transmitting code impulses from said signal transmitting set to cathode-anode circuits of the set of gas filled 7 restoring to a condition existin means for transmitting code impulses from said signal transmitting set to said positions, a set of gas filled tubes operated progressively by said code impulses for energizing the sets of gas filled tubes at each of said positions and means controlled by the operation of each of said progressively operated gas filled tubes for deenergizing the set of tubes at a preceding position.

4. A signaling system comprising a signal transmitting set, a transmission line connected to said signal transmitting set and extending to a lurality of ositions at an oflice, individual lines at eac of said positions, a set of gas filled tubes at each of said positions, means at each of said positions or connecting the individual line thereat to said transmission line over the cathodeanode circuits of the set of gas filled tubes thereat, means for transmit-tin code impulses of a predetermined lengt fromsaid signal transmitting set to said positions, a second set of gas filled tubes connected in series for controlling the operation of said firstmentioned sets of gas filled tubes at each of said positions, and means for introducing a delayin the operation ofeach of the gas filled tubes of said second mentioned set of tubes, said delay being of a duration less than the length of said code impulses but over half thereof whereby said tubes of said second set will operate progressively on successive code impulses.

5. A signaling system comprising a signal transmitting set, a transmission line connected to said signal transmitting set and extendin to a lurality of positions at an ofiice, in ividua lines at each of said positions, a set of gas filled tubes at each of said positions, means at each of said positions for connecting the, individual line thereat to said transmission line over the tubes thereat, means for transmittm impulses from said signal transmitting set to said ositions, a series of gas filled tubes operated progressively by successive ones of said code impulses for progressively operat ing the sets of gas filled tubes at each of said positions, and means associated with the last one of said series of gas filled tubes for beforethe transmission of any code impu s the gas filled tubes of said sets and said series.

6. A signaling system comprisin a signal transmitting set, a transmission ine con-s nected to said si al transmitting set and extendin to a p urality of sitions at an ofiice, in ividual lines at eac of said sitions, a set of gas filled tubes at eac of said positions, means at each of said positions for connecting the. individual line thereat to said transmission line over the cathode-anode circuits of the set of gas filled tubes thereat, means for transmitting code impulses from said signal transmitting set' to said ositions, a series of gas filled tubes operated progressively by successive ones of said code impulses for progressively operating the sets of, gas filled tubes at each of said positions, means controlled b the op eration of the last one of said series of gas filled tubes for deenergizing all of said gas filled tubes in a state of o ration, and means for introducing a time lin in the operation of deenergization of sai last one of said series of gas filled tubes.

7. A signaling system comprising a signal transmitting set, a transmission line connected tosaid signal transmitting set and extendin to a plurality of positions at an ofiice, 1ndividual lines at each of said positions, a set of gas filled tubes at each of said positions, means at each of said positions for connecting the individual line thereat to said transmission line over the cathode-anode circuits of the set of gas filled tubes thereat, means for transmitting code impulses from said si al transmitting set tosaid ositions, a serles of gas filled tubes operated progressively'by successive ones of said code impulses for controllin the operation of the sets vof gas filled tu s at each of said positions, and a gas filled tube for repeating the code impulses transmitted from said signal transmitting set to said sefice, individual lines at each of said posi-.

tions, means at each of said positions for connecting the individual line thereat to said transmission line over the cathodeanodecircuits of the set of gas filled tubes thereat, means for transmitting code impulses from said signal transmittin said positions, a series of gas filled tu s operated rogressivel by successive ones of said cod impulses or controllin the operation of the sets of gas filled tu at each of said positions, and means for repeating the code impulses transmitted from said signal transmitting set to said series of progressively operated gas filled tubes, said last mentioned means comprising a gas filled tube having its grid voltage controlled by the alternating potential drop of the current used for said code impulses, a source of alternating current of a frequency higher than that used for said code impulses, means for applying current from said last mentioned source to the cathode-plate circuit of said gas filled repeater tube, a resistance in said cathode-plate circuit, and means for utilizing the alternating voltage drop across said resistance for controlling the voltage on the set to' grid of the first tube in said series'of progressively operated gas filled tubes.

cuit whereby the alternating voltage drop 9'. A source of alternating current, a line,

switching nieans for applying pulses of current from said source to said line, a. gas

filled tube having its "input circuit connect.

ed to said line, a resistance in said input cirof current from said source may be utilized to control the voltage on the grid of said tube, a secondsource of alternating current of a frequency higher than that of the alternating current'from-said first source, means for applying current from said second source to the cathode-anode circuit of said gas filled tube, a resistancein said cathodeanode circuit, and means for" applying to a work circuit the alternating voltage drop across said'resistance of the alternating current from said second source.

In testimony whereof, I have signed my name-to this specification this 17th day of August. 1932. 1 CHARLES s. DEMARESTZ- 

